Production of deep drawn pressings

ABSTRACT

Wrinkle free deep drawn shells are formed from aluminium foil and other similar materials by employing a tapered die and a punch having a radially compressible elastic or hydropneumatic element at the nose end of the punch, such element having initial dimensions approximately equal to those of the die mouth.

G UIIIIQd States Patent [191 [111 3,724,247

Page 1 Apr. 3, 1973 541 PRODUCTION OF DEEP DRAWN 2,326,990 8/1943 Woodson ..72/62 PRESSINGS 2,037,795 4/1936 Johnson 2,662,499 12/1953 Lyon [75] Inventor: Clifford Frank Page, Banbury, En- 2,606,516 52 Raynes gland 731,367 6/1903 Huber 4 4 W'l [731 Assignee and Devehlmem 5334:4 52 16/1327 Mei i; ..72 34s Montreal, Quebec, Canada Filed: y 1971 FOREIGN PATENTS OR APPLICATIONS 1 pp No: 147,380 659,408 2/1929 France ..72/62 Primary Examiner-Richard J. Herbst 30 Foreign Application p i Data AttorneyRobert S. Dunham, P. E. Henninger, Lester W. Clark, Thomas F. Moran, Christopher C. Dunham June 2, 1970 Great Britain ..26,662/70 and Robert Scobey [52] [1.8. CI ..72/60, 72/347 57 S R C [51] Int. Cl. ..B2ld 28/18 [58] Field of se-archwn/sd" 57 60, 61, 62, 34749; Wrinkle free deep drawn shells are formed from alu- 113/120 H minium foil and other similar materials by employing a tapered die and a punchhaving a radially compressi- [56] References Cited ble elastic or hydropneumatic element at the nose end of the punch, such element having initial dimensions UNITED STATES PATENTS approximately equal to those of the die mouth.

946,962 1/1910 Grahan ..72/60 6 Claims, 7 Drawing Figures PAIENTEDAFR3 I973 3,724,247

SHEET 1 OF 4 /NV/VTOP. CLl FFORD FRANK PAGE PAIENTEDAPRB I973 3.724 247 sum 2 UF 4 PRODUCTION OF DEEP DRAWN PRESSINGS The present invention relates to the production of deep drawn shells from light gauge metal, including aluminum and aluminum alloys. The metal may be lacquered or laminated with a plastic film, such as a coating of polyethylene or polypropylene.

It is well known to produce deep drawn shells, having inwardly tapering sides, for use as baking tins and other culinary uses, since this expedient permits the cooked product to be extracted from the tin without excessive damage. The taper may be a straight taper or alternatively the side walls may have a curving taper, as ina conventional pudding bowl.

It is well known to produce disposable containers with tapered walls from aluminum foil, but these containers suffer from the defect of having severelywrinkled sides. It is also well known to produce aluminum baking tins with an unwrinkled tapered side wall but these are produced in a two-stage operation. In the first stage a shell, having a perpendicular side wall, is produced by a deep drawing operation, whilst in the second stage the side wall is reformed to impart the desired taper.

It is an object of the present invention to provide a method of and apparatus for forming a container shell, having an unwrinkled tapered side wall, from light gauge metal by a single operation or in a reduced number of operations. In particular it is an object of the invention to provide apparatus for the achievement of such result when deep drawing metal sheet in a wide range of thickness, typically from 0.0002 0.1 inches (0.005 2.5 mms). It is well known to use metal sheet in the thickness range of 0.004 0.036 inches (0.01 0.9 mms) for the production of many packaging and kitchen articles, such as bottle closures, light boxes and cans.

For the purpose of easy extraction of the contents, stackability and appearance, it is unnecessary to employ a large angle of inclination for the side wall of an aluminum container, an angle of 3 5 usually being perfectly acceptable for this purpose. However, angles up to about 13 are sometimes required. The depth of the container is usually in the range of l 3 inches, so that the difference in size between the bottom of the container and its mouth will be quite small.

In drawing light metal, such as aluminum sheet of the thickness indicated above it is essential to restrict the wall of the shell between the punch and the die to avoid wrinkling. In drawing shells with perpendicular walls,

there is no difficulty in ironing out any incipient wrinkles by restricting the clearance between the punch and the die to a distance approximating to the thickness of the sheet. If an attempt is made to draw thin light metal sheet with a punch having a size smaller than the mouth of the die, there is a tendency for the intemally-unsupported side wall of the shell to become wrinkled if the spacing between the die side wall exceeds five thicknesses of the metal for a soft metal, such as commercial purity aluminum or exceeds about two thicknesses for harder metals.

A method of deep drawing tapered receptacles from thin sheet metal has already been proposed in U.S. Pat. No. 3,344,646. In this method a tapered punch is employed in conjunction with a die, which incorporates a ring is made of nylon or teflon and strokes the outer surface of the work at a position close to the mouth of the die as it is drawn into the die. The arrangement is claimed to remove the wrinkles formed in drawing thin sheet by the operation of the punch. U.S. Pat. No. 3,344,646 also suggests that the ring might be carried in the punch without disclosing in what manner it should be arranged to effect the desired work-stroking action.

In contrast to the method of U.S. Pat. No. 3,344,646, the method of the present invention relies on the use of a punch which maintains the metal in close conformity with the die wall by the exercise of hydraulic or elastohydraulic pressure around the periphery of the nose of the punch so that the effective dimensions of the punch nose progressively decrease as it progresses into the tapered die.

The present invention enables a deep drawn shell, having a tapered side wall, to be produced from light gauge metal by arranging that the die has a tapered inside wall and that the punch has a side wall which can remain in close conformity with the side wall of the die whilst drawing sheet metal into the die mouth. In order to do this the side of the punch is comprised by a member,'the nose end of which initially of dimensions substantially equal to that of the die mouth and which can yield under the compressive force exerted by the flexible U-section ring in its side wall. The U-section side wall of the die whilst exerting substantial reaction force through hydraulic or elasto-hydraulic pressure. The punch side must be such that it doesnot yield readily under the forces exerted on it as the result of the drawing action of the punch on the metal sheet and the minimum force under which the punch side may yield is dependent to large extent on the thickness and physical properties of the sheet, which the punch is designed to draw.

It is well known that rubber and other elastomeric materials will flow under pressure in a manner analogous to a hydraulic fluid and will revert to a normal shape when the pressure is relaxed. Providing that there is space for displaced material to flow into, a firmly located elastomeric ring can be compressed radially without wrinkling and will, during such compression, exert a substantial elasto-hydraulic pressure against the surface by which it is compressed.

In consequence the side of the punch is preferably formed of a member of rubber (which term is employed herein to cover other elastomeric materials), arranged in a recess in the punch and which initially has dimensions at its nose end corresponding to the dimensions of the die mouth. For example, the punch may be provided with a massive rubber member, having a truncated-V cross-section and arranged in a correspondingly shaped groove. A space is left between the base of the rubber member and the bottom of the groove to provide room for the rubber to flow into when its outer surface is pressed inwardly by the tapered die wall. Preferably, one edge of the'rubber than at the nose end because there is some tendency of rubber, displaced by compression of the nose end, to

roll down towards the tail end. As an alternative the I rubber member may be formed of a series of parts arranged end-to-end and separated by rigid metal spacers of sightly smaller diameter.

In another arrangement an appropriately shaped rubber member is arranged in the groove and is backed by resilient means such as a series of springs or an annular bag filled with gas under high pressure with a hydraulic liquid in communication with a mass of gas,

as in a hydraulic pressure accumulator.

periphery of the punch and which may be considered as a single member for the present purpose.

In a still further arrangement the nose end of the punch is formed of a shaped envelope made of a somewhat resilient plastics material, such as polyurethane, filled with a hydraulic fluid which is in communication with an enclosed mass of gas to permit some hydraulic fluid to be displaced from said envelope against gas pressure.

Various forms of apparatus according to this invention are illustrated in the accompanying drawings,

wherein:

FIG. 1 is a section of one form of punch,

FIG. 2 is a section of an alternative form of punch,

FIG. 3 is a section of a die for use with the punch of FIG. 1 or 2,

FIG. 4 is a section of a die set incorporating the punch and die,

FIG. 5 is a vertical section illustrating two alternative forms of punch,

FIG. 6 is a vertical section illustrating a further form of punch, and

FIG. 7 is a vertical section illustrating a still further form of punch.

The die 1 shown in FIG. 3 has an annular top end 2 which leads through a radiused corner 3 into sides 4, which are tapered at an angle of about 4. At the mouth of the die there is an edge surface 5, leading into an inclined face 6.

The punches shown in FIGS. 1 and 2 have a nose 11, which has a flat surface 12 leading via a rounded corner into a tapered side wall 14. The diameter of the surface 12 is slightly less than that of the end 2 of the die and the taper angle of the side wall 14 of the punch is the same as the taper angle of the sides 4 of the die.

A V-groove 15 is cut in the side wall 14 of the punch and occupies substantially the whole length of the side wall. In this is located a V-shaped rubber member 16' having an outer surface 17, which in its normal condition' has substantially the same diameter as the mouth of die 1. A space 18 between the inner periphery of the member 16 and the bottom of the groove is available for flow of the rubber when subjected to compression by the inward relative movement of the punch and die. In this arrangement it will be seen that the rounded edge 17a of the rubber member 16 is located at only a small distance to the rear of the head end surface 12 of the punch and, in efiect, is initially the peripheral edge of the punch nose. It is at this edge 17a that the drawing of the sheet material commences. The material used for the rubber member 16 should be resistant to abrasion and, as far as possible, self-lubricating. As an example, a suitable material for use in conjunction with a conventional aluminum alloy employed for can-making has the following properties:

Durometer Reading 92 Tensile Strength 5500 pounds/square inch Modulus at 200% 1200 pounds/square inch Ultimate Elongation 600% Polyurethane materials having properties within these ranges are sold by Avon Rubber Co., Ltd., Melksham, Wiltshire, England, under the name Avothane. This material would be too hard for soft aluminum foils and insufficiently hard for harder and tougher metals. The elastomeric material used in the die must be selected in accordance with the duty which the die is to perform.

, In this arrangement it will be seen that the rubber member 16 is clamped between the nose l1 and a cooperating ring 11a by the threaded engagement of the nose 11 with a base part 11b. Thus it is possible to prestress the rubber member 16 by tightening down the nose 11.

In the alternative construction illustrated in FIG. 2 the member 16 is replaced by an insert 20, which communicates with an oil supply gallery 21. An elastic envelope member 22 is bonded to the insert 20 and its periphery moves between the dotted line position, which it assumes when it is free from confinement by the die, and the full line position. The oil is maintained under pressure which gradually increases as the oil is expelled through the oil supply gallery.

The die of FIG. 3 and the punch of FIG. 1 are shown assembled into an otherwise conventional die set in FIG. 4. The die set illustrated in this figure is intended for the production of container shells at high speed from continuous strip material, a flat blank being punched out of the strip in the first stage of the press movement, the blank being drawn by the illustrated punch and die in the second stage and finally trimmed at the end of the press stroke.

In FIG. 4 the parts of the die set are shown respectively at the top and bottom of their travel in the right and left half of the figure.

The punch 11, 11b is mounted on a bottom platen 30, on which is also mounted a blanking die 31. Between the punch 11, ilb and blanking die 31 is a blankholder 32, pressed upwardly against a shoulder on blankholder 32 by spring-loaded pressure pins 33, and a trimming die 34. The die 1 (which is somewhat modified as compared with FIG. 3) is mounted within a blanking punch 35 secured to an upper platen 36 and is backed by a resiliently compressible disc 37. An ejector 38 is mounted within the die 1 anda spring-loaded stripper 39 is motmted around the blanking punch 35. Thus the first efiect of the downward movement of the platen 36 is to blank out a disc having a diameter equal to the internal diameter of the blanking die 31. This disc is then gripped between the blanking punch 35 and the blankholder 32 as the drawing die l and punch 11,

1 1b co-operate to effect the deep drawing operation in an essentially conventional manner, the punch 11, 11b and die co-operating in the manner already described above.

In the construction of FIG. 5 the punch comprises a central shaft 40, having a head 41. Head 41 has an inclined underneath surface 42, which is in contact with a corresponding surface 43 on a ring-shaped rubber member 44. The rubber member 44 also has an inclined surface 45, which contacts a surface 46 on a slider 47, which is pressed upwardly axially by springs 48. The slider 47 is maintained concentric with the shaft 41 by engagement of its tail 49 with a stationary guide 50. The tail 48 of the slider 47 may slide on the outside of the guide 49 as shown in the right-hand side of FIG. 5. Alternatively the slider 47 may have a tail 49, which is guided in a bore inside the guide 50', within which the springs 48 are housed, as shown in the left-hand side of FIG. 5.

It will readily be understood that as the member 44 moves progressively into a tapered die, the rubber at the upper or leading end of the member 44' is progressively compressed in the radial direction into the radially tapering zone lying between the surfaces 42 and 46. The wedge-action thus occasioned leads to axial displacement of the member 47 against the biasing force provided by the springs 48.

In all the punches illustrated in FIGS. 1, 2, 4-and 5 the nose end of the punch may be vented to atmosphere in known manner to ensure separation of the punch from the shell during the return stroke.

As compared with the apparatus of the present invention the apparatus of US. Pat. No. 3,344,646 suffers from the disadvantage that at the beginning of the punch stroke the gap between the punch and the rigid die mouth is of necessity large, because the ring in the die wall exerts no influence at the beginning of the punch operation. The force which the nylon ring can exert on the metal is comparatively small and it would be impossible to replace it by a ring of hard rubber or polyurethane because of their lack of self-lubricating properties and the resultant greater friction force between the metal sheet and the ring as compared with the present invention in which the rubber ring forms part of the punch.

In the punch of FIG. 6 the nose of the punch is formed by a thick-walled polyurethane envelope 60. For example, the wall thickness may be about Mr inch (0.63 cms). The envelope 60 is secured to a punch base 61 by means of a threaded ring 63, engaged by a hollow bolt 64, rotatable in relation to the base 61. The envelope 60 is provided with an appropriately thickened tapered portion 65 engaged between ring 63 and a dished surface 66 on base 61. The space within envelope 60 is filled with hydraulic fluid and this communicates with a hydraulic accumulator (not shown) via galleries 67 in the bolt 64 and the space within the base 61.

The envelope 60 is so dimensioned that the diameter of its side wall, after pressurization of the hydraulic accumulator is approximately equal to the mouth diameter of the die.

Since pressurization of the envelope 60 would tend to dome its nose end unless some reinforcement were provided a rigid nose piece 68 is secured in the nose of the end envelope by the engagement of a threaded portion with a nut 69. The nose piece 68 is slidably mounted in the bolt 64 and is biased downwardly by spring washers 70, which press down against an abutment ring 71. The nose end of the punch is vented to atmosphere via vent passage 72 in the stem of the nose piece and a flexible vent pipe 73 secured to the stem of nose piece 68. It will be noted that the peripheral diameter of the nose piece is considerably smaller than that of the nose end of the envelope 60. When the nose end of the envelope progresses into the die and in consequence is reduced in diameter, the nose piece 68 tends to rise in relation to the base 61, compressing the washers and thus allowing the side wall of the envelope to elongate to provide space into which displaced material from the envelope may flow.

A still further form of punch is illustrated in FIG. 7. In this Figure the punch is formed by a substantially cylindrical rubber member having a wall thickness of at least 7% inch (1.25 cms). The diameter of the nose end of the member 80 is substantially equal to that of the die mouth and slightly exceeds the diameter of the bottom or tail end. The member 80 is provided with a thickened flange 81 which'is' clamped against a dished surface 82 of the die base 83 by a stud 84, provided with a vent passage 85. The periphery of the stud 84 is slightly relieved at 86. It is only the portion of the member 80 at and above the relieved portion 86 which is intended to enter-the die.

The recess in the nose end of the member provides space to receive material displaced by the compression of the thick rubber wall. Whilst it may be cylindrical as illustrated, it may also be slightly conical.

Whilst the punch illustrated in FIG. 7 is satisfactory for some purposes it has the disadvantage that it is incapable of producing any form of embossing of the bottom of the shell.

Whilst the various forms of punch and die sets illustrated in this specification are intended for drawing containers of circular section, the principles of the invention are equally applicable to punch and die sets for drawing oblong and rectangular shells and even to shells with multiple recesses.

I claim:

1. A punch and die set for the production of deep drawn shells having tapered side walls from thin metal sheet or foil comprising a die having a tapered side wall which tapers progressively from its mouth inwardly to smaller dimensions at its end remote from the mouth, and a punch which has a side wall formed by a member capable of yielding under compressive force and exerting substantial hydraulic or elasto-hydraulic pressure in reaction to compressive force, said member when free from peripheral compressive force, having at least at its nose end substantially the dimensions of the die mouth, said punch and die being mutually shaped for substantial drawing of the sheet or foil axially of the punch by movement of the punch into the die to the end thereof while said member compressively holds the sheet or foil against the die wall.

2. A punch and die set according to claim 1 in which the side wall member comprises a solid rubber member arranged in a groove in the'side wall of a punch having portion corresponding in dimensions with the die mouth, the peripheral dimensions of at least the nose end of said rubber member, when free from peripheral compressive force, corresponding to the dimensions of the die mouth.

3. A punch and die set according to claim 1 in which the punch is composed of a solid rubber member confined between a rigid head member and a tail member, the head member being smaller in dimension than the end of the die remote from the mouth, a portion of the rubber member being exposed around the periphery of the head member to define the periphery of the nose end of the punch.

4. A punch and die set according to claim 3 in which the rubber member is subjected to a predetermined axial loading pressure, when free from peripheral compressive force, by means of an axially slidable tail member, subjected to an axial biasing load.

5. A punch and die set according to claim l in which the nose end of the punch is composed of a thick walled elastic envelope, filled with hydraulic fluid in communication with an enclosed mass of gas, the said envelope being secured to the tail of the punch and having a side wall, which when free from compresive force, has dimensions corresponding to the die mouth.

6. A punch and die set for the production of deep drawn shells having tapered side walls from thin metal blanks, comprising a die and having a side wall which tapers progressively from its mouth inwardly to its remote end substantially without widening at any place, and a punch which has a side wall formed by a member capable of yielding under compressive force and exerting substantial hydraulic or elasto-hydraulic pressure in reaction to compressive force, said member when free from peripheral compressive force, having at last its nose end with substantially the dimensions of the die mouth, said member being shaped substantially to fit into said mouth and being subjected to radial compressive force substantially only on axial movement of the punch within said tapered wall, said punch having a rigid head member of dimensions smaller than the nose end of the punch wall member, and tail means, said wall member being held between said head member and said tail means, and said punch and die being mutually shaped so that movement of the punch against the blank into the die effects substantial drawing of thebla nlk axially until said head member causes the drawn blank to approach the remote end of the die,- while said wall member holds the metal of the blank compressively against the tapered wall of the die. 

1. A punch and die set for the production of deep drawn shells having tapered side walls from thin metal sheet or foil comprising a die having a tapered side wall which tapers progressively from its mouth inwardly to smaller dimensions at its end remote from the mouth, and a punch which has a side wall formed by a member capable of yielding under compressive force and exerting substantial hydraulic or elasto-hydraulic pressure in reaction to compressive force, said member when free from peripheral compressive force, having at least at its nose end substantially the dimensions of the die mouth, said punch and die being mutually shaped for substantial drawing of the sheet or foil axially of the punch by movement of the punch into the die to the end thereof while said member compressively holds the sheet or foil against the die wall.
 2. A punch and die set according to claim 1 in which the side wall member comprises a solid rubber member arranged in a groove in the side wall of a punch having a nose portion corresponding in dimensions with the end of the die remote from the mouth and a tail end portion corresponding in dimensions with the die mouth, the peripheral dimensions of at least the nose end of said rubber member, when free from peripheral compressive force, corresponding to the dimensions of the die mouth.
 3. A punch and die set according to claim 1 in which the punch is composed of a solid rubber member confined between a rigid head member and a tail member, the head member being smaller in dimension than the end of the die remote from the mouth, a portion of the rubber member being exposed around the periphery of the head member to define the periphery of the nose end of the punch.
 4. A punch and die set according to claim 3 in which the rubber member is subjected to a predetermined axial loading pressure, when free from peripheral compressive force, by means of an axially slidable tail member, subjected to an axial biasing load.
 5. A punch and die set according to claim 1 in which the nose end of the punch is composed of a thick walled elastic envelope, filled with hydraulic fluid in communication with an enclosed mass of gas, the said envelope being secured to the tail of the punch and having a side wall, which when free from compressive force, has dimensions corresponding to the die mouth.
 6. A punch and die set for the production of deep drawn shells having tapered side walls from thin metal blanks, comprising a die having means closing its remote end and having a side wall which tapers progressively from its mouth inwardly to its remote end substantially without widening at any place, and a punch which has a side wall formed by a member capable of yielding under compressive force and exerting substantial hydraulic or elasto-hydraulic pressure in reaction to compressive force, said member when free from peripheral compressive force, having at least its nose end with substantially the dimensions of the die mouth, said member being shaped substantially to fit into said mouth and being subjected to radial compressive force substantially only on axial movement of the punch within said tapered wall, said punch having a rigid head member of dimensions smaller than the nose end of the punch wall member, and tail means, said wall member being held between said head member and said tail means, and said punch and die being mutually shaped so that movement of the punch against the blank into the die effects substantial drawing of the blank axially until said head member causes abutment of the drawn blank against the closing means at the remote end of the die, while said wall member holds the metal of the blank compressively against the tapered wall of the die. 